1. Field of the Invention
The present invention relates to data compression, and more particularly, to an encoding method and apparatus of deformation information of a 3-dimensional (3D) object.
2. Description of the Related Art
3-dimensional (3D) presentation is known, for example, to be utilized in computer games or virtual reality world environments in a computer system. In the case of 3D models, a Virtual Reality Modeling Language (VRML) has been the primary means for expressing 3D objects.
In VRML, a 3D object is expressed in the form of a polygonal mesh, and animation of the object is accomplished by a linear key framing method. In this animation method, a predetermined key frame is set on an arbitrary time axis, and animation data between each key frame is interpolated by a linear interpolation method. A key frame used in this method is defined by an interpolator node, which is formed of field data, expressed as key data indicating the position of the key frame on a time axis, and key value data indicating attribute information of the key frame at a corresponding key.
Meanwhile, when smooth animation similar to an actual moving body is expressed by the key framing method having the characteristic of piecewise liner interpolation, a large amount of key frame information should be provided through interpolator nodes, which causes a serious problem in cost and efficiency. When the key framing method is used off-line, a large capacity storage apparatus is needed to store the huge amount of 3D animation data. When the key framing method is used on-line, in addition to the large capacity storage apparatus, transmission of 3D animation data from a server to terminals requires very high speed and large capacity transmission routes, and data reliability is lowered in line with the increasing probability of transmission error. Therefore, an efficient compressing and encoding method is needed in order to reduce the amount of interpolator node data.
For this, a Differential Pulse Code Modulation (DPCM) encoding method is used as shown in FIG. 1. In the DPCM method, only the difference value of data is encoded so that the number of bits decreases. The DPCM method is used in compressing data coupled with the key framing method. Also, the DPCM method is used in the MPEG-4 Binary Format for Scene (BIFS).
Referring to FIG. 1, a parser 105 identifies data information of an interpolator node to be encoded. A demultiplexer 110 classifies field data of the interpolator node to be encoded among interpolator nodes. More specifically, the demultiplexer receives a Coordinate Interpolator (CI) node from the parser 105, and outputs field data formed of a key (QK) and key values (QKV) corresponding to the node. A DPCM processor 120 receives field data of the CI node, divides the key and key values, and removes temporal redundancy among data, by generating each differential value (EK, EKV) of neighboring keys and key value data.
FIG. 2 is a detailed diagram of the DPCM processor of FIG. 1. Referring to FIG. 2, when a differential value of a value to be encoded at present is generated, an inverse quantizer 122 makes the previous data on the time axis the same as a value reconstructed in a decoding apparatus 150. Referring to FIG. 1 again, a quantizer 130 receives thus generated differential values (EK, EKV), and adjusts the expression precision degree of data to be encoded so as to provide data compression effects. An entropy encoder 135 receives values ( ) quantized in the quantizer 130, removes redundancy among bits with respect to the probability of symbol occurrence, and generates a compressed bit stream 140. The bit stream 140 generated by the encoding apparatus 100 of FIG. 1 is reconstructed to the CI node, which was encoded, by the decoding apparatus 150 which performs the inverse of the process performed by the encoding apparatus 100.
However, in removing data redundancy existing in the field data of the interpolator node, the encoding apparatus 100 and decoding apparatus 150 having the above-described structures only removes data redundancy with respect to spatial correlation of vertices forming the shape of the 3D object. Thus, data redundancy with respect to temporal correlation, which occurs greatly in the key framing type animation, is not considered at all, and therefore it is difficult to improve the actual compression effect.